Low dielectric constant materials are used as interlayer dielectrics in microelectronic devices, such as semiconductor devices, to reduce the RC delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between metal lines must also decrease to maintain the improvement. Certain low-k materials have been proposed, including various carbon-containing materials such as organic polymers and carbon-doped oxides. Although such materials may serve to lower the dielectric constant, they may offer inferior mechanical properties such as poor strength and low fracture toughness. The eventual limit for a dielectric constant is k=1, which is the value for a vacuum. Methods and structures have been proposed to incorporate void spaces or “air gaps” using, for example, sacrificial materials, in attempts to obtain dielectric constants closer to k=1. One major issue facing such technologies is how to remove sacrificial material from relatively small or relatively large volumes to facilitate multi-layer structures with voids. Another major issue facing such technology is how to facilitate void creation while providing a structure which can withstand modern processing treatments, such as chemical-mechanical polishing and thermal treatment, as well as post processing mechanical and thermo-mechanical rigors.
Accordingly, there is a need for a microelectronic structure incorporating voids which has low-k dielectric properties, can be used in multi-layer structures, and has acceptable mechanical characteristics during and after processing.